Question: If $5a + b = 7$ and $x + 8y + 3z = 8$, what is $-9z - 24y - 3x + 45a + 9b$ ?
Solution: $= 45a + 9b - 3x - 24y - 9z$ $= (9) \cdot (5a + b) + (-3) \cdot (x + 8y + 3z)$ $= (9) \cdot (7) + (-3) \cdot (8)$ $= 63 - 24$ $= 39$